The present invention generally relates to packaging and more particularly is directed to a rotating stretch wrapping apparatus for making unitary packages which hold a plurality of components, each package containing a load wrapped in a web of stretched film.
Case packing or boxing is a common way of shipping multiple unit products. Multiple unit products are generally stacked in a corrugated box or are wrapped with kraft paper with the ends of the kraft paper being glued or taped.
Some manufacturers use strapping of vertical steel or plastic binding to unitize the product. The problems incurred in the use of strapping are the requirement of costly corner protectors, danger of bending or snapping and injuring the operator while applying this high tension material to the loads, the ever present problem of settling due to moisture wetting the cartons, and the sides bulging or normal vibrations causing the straps to loosen and the load to come apart.
Glue is an alternative method used in some areas, but customer dissatisfaction with gluing is high because removal of glued cartons or bags from the unitized loads tends to tear outside layers of the cartons. Glue, although an inexpensive material, demands interleaving for product orientation and thus requires more durable and expensive packaging material.
Because of the lack of alternatives of packaging, tape is currently being used to horizontally bind the top layer of the load. However, tape is expensive and allows relatively free movement of all products surrounded.
Another way of shipping products is by putting a sleeve or covering of heat shrinkable material around and products and shrinking the sleeve to form a unitized package. The use of heat shrinkable film is described in U.S. Pat. Nos. 3,793,798; 3,626,645; 3,590,549 and 3,514,920. A discussion of this art is set forth in U.S. Pat. No. 3,867,806.
An economical way of packaging products is by wrapping the product load with a web of stretched plastic film.
The elasticity of the stretched plastic film holds the products of the load under more tension than either shrink wrap or kraft wrap, particulaly with products which settle when packaged. The effectiveness of stretched plastic film in holding a load together is a function of the containment or stretch force being placed on the load and the ultimate strength of the total layered film wrap. These two functions are determined by the modulus or hardness of the film after stretch has occurred and the ultimate strength of the film after application. Containment force is currently achieved by maximizing elongation until just below a critical point where breaking of the film occurs.
The use of wrapping machinery to wrap stretched film around a load is well known in the art. Four types of stretch wrapping apparatus are commonly used in the packaging industry and these types are generally described as spiral rotary machines, full web rotary machines, passthrough machines, and circular rotating machines.
A typical spiral machine is shown in U.S. Pat. No. 3,863,425 in which film is guided from a roll and wrapped around a cylindrical load in a spiral configuration. A carriage drives the film roll adjacent the surface of the load to deposit a spiral wrap around the load and returns in the opposite direction to deposit another spiral overwrap around the load.
Spiral wrapping machines which are currently commercially available are manufactured by Lantech, Inc. under Model Nos. SVS-80, SVSM-80, STVS-80, STVSM-80 and SAHS-80.
A full web type of apparatus which wraps stretched film around a rotating load is disclosed in U.S. Pat. No. 3,876,806 assigned to Lantech, Inc. A similar full web apparatus using a tensioned cling film wrapped around a rotating load is shown by U.S. Pat. No. 3,986,611 while another apparatus using a tacky PVC film is disclosed in U.S. Pat. No. 3,795,086.
Full web wrapping machines typical of those presently commercially available are Model Nos. S-65, T-65 and SAH-70 manufactured By Lantech, Inc.
Another type of machine for wrapping a pallet load commonly called a passthrough machine is disclosed in U.S. Pat. No. 3,596,434. In this reference a pallet load is transported along a conveyor and the leading face of the pallet load contacts a vertical curtain of film formed by the sealed leading edges of film webs dispensed by two rolls of film on opposite sides of the path of the pallet load. The pallet load continues to move along the conveyor, carrying with it the sealed film curtain until the side faces of the pallet load as well as the front face are covered by film web. A pair of clamping jaws then close behind the pallet load, bringing the two film web portions trailing from the side faces of the pallet load into contact with one another behind the pallet. The jaws then seal the film web portions together along two vertical lines, and cut the web portions between those two seals. Thus, the film web portions are connected to cover the trailing face of the pallet load, and the film curtain across the conveyor is re-established to receive the next pallet load. The pallet load may subsequently be exposed to heat in order to shrink the film web thus applying unitizing tension to the load, as is disclosed in U.S. Pat. No. 3,662,512. Commercial passthrough machines are currently manufactured by Weldotron, Arenco, and SAT of France.
Various apparatus and processes have been developed to rotatably wrap stacked components to form a load.
Stationary loads which are brought to a loading area and are wrapped by a rotating member which dispenses stretched film around a load are disclosed in U.S. Pat. Nos. 4,079,565 and 4,109,445. U.S. Pat. No. 4,079,565 discloses a full web vertical wrap of the load while U.S. Pat. No. 4,109,445 discloses the horizontal spiral wrap of a load. U.S. Pat. No. 4,050,220 discloses a wrapping device for multiple unit loads. Each load is conveyed to a wrapping area in which a load is supported on one or more stationary planar surfaces. The leading edge of a roll of stretchable plastic wrapping material is held adjacent to the load, and the roll of material is rotated about the load and the supporting planar surfaces, wrapping the load and the supporting surfaces together. Plastic wrapping material is stretched during the wrapping operation so that the material is under tension when applied to the load. After the wrapping cycle is complete, the load is pushed past the ends of the supporting surfaces, and the wrapping material which covered the supporting surfaces collapses against the supported sides of the load. Further developments of this wrapping system are disclosed in U.S. Pat. Nos. 4,110,957 and 4,178,734.
U.S. Pat. No. 603,585 discloses a spiral wrapping device for enclosing individual newspapers in paper wrap for mailing purposes. Each newspaper is placed on a cylindrical core with a circumference approximately twice that of a newspaper, and each newspaper advances along the length of the core as the core is rotated. Wrapping paper is applied to the core at an angle and the wrapping paper between newspapers is severed as each newspaper reaches the end of the cylinder and is placed on a flat horizontal surface, thereby collapsing the wrapping paper against the underside of the newspaper previously pressed to the cylinder.
U.S. Pat. No. 1,417,591 discloses a wrapping machine for individual times such as boxes in which each such item is conveyed along the surface of a horizontal sheet of wrapping material. The edges of wrapping material on each side of an item are curled upward to meet one another atop the item to be wrapped thereby forming a tube around the item. The leading end of the tube is sealed and the trailing end of the tube is severed and then sealed to enclose the item. Another device which utilizes this system of wrapping is disclosed in U.S. Pat. No. 3,473,288.
In U.S. Pat. No. 2,575,467, a wrapper of cylindrical packages for material such as sausage is disclosed in which the package is rotated about its cylindrical axis as wrapping tape is applied at an angle to form a cylindrical wrap.
In U.S. Pat. No. 2,863,270 two cylindrical items of approximately equal diameter are abutted at their planar ends, and placed by hand in a cradle which exposes the complete circumference of the abutting ends. A roll of wrapping material is then driven by a hand crank mechanism to circulate around the circumference of the abutting ends, applying wrapping material thereto. When sealed together, the pair of cylindrical items are removed from the cradle by hand.
A spiral wrapping machine for long bundles of items such as filaments is disclosed in U.S. Pat. No. 3,000,167. As the bundle of filaments moves along its axis through the wrapping area, a ring circulates about the bundle carrying a roll of wrapping material which is applied to the bundle to form a spiral wrap pattern. Because the normal load of filaments or similar items is much longer than the wrapping area, it is not necessary to provide support for the bundle in the wrapping area, and therefore no support structure is wrapped with the bundle.
All of these prior art apparatuses suffer from a severe limitation which relates to cost per unit load for film unitization. Friction brake devices do not maintain a consistent stretch force on the film. These brake devices are subject to variation due to their physical construction, sensitivity to speed change caused by passage of load corners, and the resultant sudden acceleration and deceleration of film payout. A typical 40".times.48" pallet load will incur a surface speed change of more than 40% with each quarter turn. Moreover, it can be appreciated that these speed changes are substantially discontinuous as film dispensed by relative rotation of the film roll around the load is intercepted by successive corners of the load. Higher rotation speed of 12-18 revolutions per minute produce additional resonating forces which change during payout and the resultant weight decrease of the film roll. Additional limitations on maximum elongation are caused by film roll imperfections and gauge variations which accentuate the force variations described above to produce film ruptures. Even though all of the films previously described carry manufactures specified elongation capabilities above 300%, these rates cannot be approached because of limitations imposed by friction-type brake devices.
Commercial circular rotating wrapping machines are presently manufactured by Lantech, Inc. under the trademark LANRINGER, and are provided with wrapping ring inner diameters of 36 inches, 54 inches, 72 inches, and 84 inches. In differentiating between the various circular rotating wrapping machines manufactured by Lantech, Inc., the manual model has the designation SR; the full web models have the designations SVR and SAVR; the multiple banding models have the designation SVBR and SAVBR; the spiral models have the designation SVSR and SAVSR, and the continuous wrap or bundler models have the model designtions SVCR and SAVCR.
U.S. Pat. Nos. 4,302,920 and 4,317,322, assigned to Lantech, Inc., discloses a pre-stretch film elongation system mounted adjacent a film roll and rotated about a stationary load. The pre-stretch system which is mounted on the rotating ring includes an upstream roller and a downstream roller across which the film web successively passes. The two rollers are speed coupled by gears, belts, or the like, which force a constant ratio of angular velocity between the rollers. Film is drawn from the film roll and across each of the rollers by relative rotation of the ring around the load. The fixed speed ratio between the upstream and downstream rollers, in which the downstream roller moves more quickly than the upstream roller, causes substantial stretching between the rollers of the web. However, it can be appreciated that the entire force exerted between the rollers is due to film being wrapped about the load. In this device the substantial changes in payout speed demand are transmitted directly from the load back through the web to the pre-stretch device, so that the level of force exerted on the film between the downstream roller and the load remains relatively constant.